U.S. patent application number 14/439374 was filed with the patent office on 2015-10-29 for method for manufacturing optical lenses and assembly for manufacturing such lenses.
The applicant listed for this patent is ESSILOR INTERNATIONAL (COMPAGNIE GENERALE D'OPTIQUE). Invention is credited to Luis CASTRO, Eric GACOIN, Jerome MOINE, Bernard PONS.
Application Number | 20150309217 14/439374 |
Document ID | / |
Family ID | 47557287 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150309217 |
Kind Code |
A1 |
CASTRO; Luis ; et
al. |
October 29, 2015 |
METHOD FOR MANUFACTURING OPTICAL LENSES AND ASSEMBLY FOR
MANUFACTURING SUCH LENSES
Abstract
A method for manufacturing an optical lens, includes the steps
of providing a blank (1) which includes an upper surface and a
lower surface (33) for forming first and second lens surfaces (2),
an edge surface (4) forming a first mechanical positioning
reference point and a ramp portion (5) provided between the edge
surface and the upper surface, which forms a second positioning
reference point; providing a positioning ring (10) including a
cavity defining an inner contour (20) concentric with the edge
surface which forms a first complementary control reference point
and a shoulder (21) forming a second complementary control
reference point; fitting the blank into the cavity, the edge
surface being in contact with the inner contour and the ramp
portion being in contact with the shoulder; and locking the blank
in position on a locking and supporting pin, the ring then being
positioned there between.
Inventors: |
CASTRO; Luis;
(Charenton-le-Pont, FR) ; GACOIN; Eric;
(Charenton-le-Pont, FR) ; MOINE; Jerome;
(Charenton-le-Pont, FR) ; PONS; Bernard;
(Charenton-le-Pont, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ESSILOR INTERNATIONAL (COMPAGNIE GENERALE D'OPTIQUE) |
Charenton-le-Pont |
|
FR |
|
|
Family ID: |
47557287 |
Appl. No.: |
14/439374 |
Filed: |
October 29, 2013 |
PCT Filed: |
October 29, 2013 |
PCT NO: |
PCT/FR2013/052590 |
371 Date: |
April 29, 2015 |
Current U.S.
Class: |
29/458 ;
228/122.1; 269/287; 29/428 |
Current CPC
Class: |
B24B 13/0055 20130101;
B23K 1/19 20130101; B29D 11/00942 20130101; G02B 3/00 20130101;
B23K 1/0008 20130101 |
International
Class: |
G02B 3/00 20060101
G02B003/00; B29D 11/00 20060101 B29D011/00; B24B 13/005 20060101
B24B013/005; B23K 1/00 20060101 B23K001/00; B23K 1/19 20060101
B23K001/19 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2012 |
FR |
1260370 |
Claims
1-18. (canceled)
19. A process for manufacturing an optical lens having a first face
(2) and a second face (3) opposite said first face (2), comprising
a step of positioning said second face (3) relative to said first
face (2) for the machining of said second face (3), which
positioning step comprises steps of: providing (131) a lens blank
(1) for forming said optical lens, which lens blank (1) has an
upper face (32) for forming said first face (2), a lower face (33),
opposite said upper face (32), for forming said second face (3),
and at least one positioning guide; providing (133) a positioning
ring (10) having at least one control guide; mounting (134) said
lens blank (1) on said positioning ring (10); positionally blocking
(135) said lens blank (1) on a blocking and holding pin (30), said
positioning ring (10) then being interposed between said lens blank
(1) and said blocking and holding pin (30); wherein said lens blank
(1) comprises a generally circular edge face (4) forming a first
mechanical positioning guide and at least one sloped portion (5)
forming a second mechanical positioning guide, said at least one
sloped portion (5) being located between said generally circular
edge face (4) and said upper face (32); said positioning ring (10)
has a generally cylindrical shape and comprises a cavity (13)
defining a generally circular internal outline (20) forming a first
complementary control guide, which internal outline (20) is
concentric with said edge face (4) of said lens blank (1), and a
shoulder (21) forming a second complementary control guide; and
said step (134) of mounting said lens blank (1) on said ring (10)
comprises the step of at least partially lodging said lens blank
(1) in said cavity (13) of said ring (10), said edge face (4) of
said lens blank (1) at least partially making contact with said
internal outline (20) of said ring (10) and said at least one
sloped portion (5) of said lens blank (1) also making contact with
said shoulder (21) of said ring (10).
20. The process as claimed in claim 19, wherein said lens blank (1)
further comprises a third mechanical positioning guide (6) in said
generally circular edge face (4), a flat for example, and said
positioning ring (10) comprises a third complementary control guide
(18, 19) in said internal outline (20), for example a right
portion, said third mechanical positioning guide (6) and said third
mechanical control guide (18, 19) being configured to immobilize
rotationally said lens blank (1) about an axis (Tz) passing through
said upper (32) and lower (33) faces of said lens blank (1),
relative to said ring (10), when said lens blank (1) is mounted on
said ring (10).
21. The process as claimed in claim 19, wherein said lens blank (1)
further comprises a third mechanical or visual positioning guide
(6) in said generally circular edge face (4) or at the periphery of
said upper face (32); and said process further comprises a step
(136) of visually or mechanically controlling the angular position
of said lens blank (1) relative to said ring (10), which angular
position is measured relative to an axis (Tz) passing through said
upper (32) and lower (33) faces of said lens blank (1), when said
lens blank (1) is mounted on said ring (10); and a step of
determining a possible angular position error.
22. The process as claimed in claim 19, further comprising a step
of machining (137) said lower face (33) of said lens blank (1) in
order to form said second face (3) of said optical lens.
23. The process as claimed in claim 22, further comprising steps
of: trimming (139) said lens blank (1) to a preset diameter;
polishing (140) said previously machined second face (3); and
engraving (141) said previously machined second face (3).
24. The process as claimed in claim 19, further comprising a step
of coating (132) said upper face (32) of said lens blank (1) before
said step of mounting said lens blank (1) on said positioning ring
(10).
25. The process as claimed in claim 19, wherein said positioning
ring (10) further comprises an injection channel (25) opening onto
said cavity (13) and said step (135) of positionally blocking said
lens blank (1) on said blocking and holding pin (30) comprises the
step of injecting a binding material (31), for example a metal,
into said injection channel (25).
26. The process as claimed in claim 19, wherein said step of
providing (131) said lens blank (1) comprises steps of: edging
(121) at least partially the outline of said lens blank (1) in
order to form said generally circular edge face (4) and thus form
said first mechanical positioning guide of said lens blank (1);
chamfering (122) at least partially one portion of said lens blank
(1), which portion is located between said generally circular edge
face (4) and said convex face (32), in order to form said at least
one sloped portion (5) and thus form said second mechanical
positioning guide of said lens blank (1); and machining (123) said
third mechanical positioning guide of said lens blank (1) into said
outline of said lens blank (1).
27. The process as claimed in claim 19, wherein said step of
providing (131) said lens blank (1) further comprises a step of
machining (110) said upper face (32) of said lens blank (1) in
order to form said upper face (2) of said optical lens.
28. An assembly comprising a lens blank (1) for forming an optical
lens having a first face (2) and a second face (3) opposite said
first face (2), and a positioning ring (10) on which said lens
blank (1) is mounted, which lens blank (1) has an upper face (32)
for forming said first face (2) and a lower face (33), opposite
said upper face (32), for forming said second face (3); wherein
said lens blank (1) further comprises a generally circular edge
face (4) forming a first mechanical positioning guide and at least
one sloped portion (5) forming a second mechanical positioning
guide, said at least one sloped portion (5) being located between
said generally circular edge face (4) and said upper face (32);
said positioning ring (10) has a generally cylindrical shape and
comprises a cavity (13) defining a generally circular internal
outline (20) forming a first complementary control guide, which
internal outline (20) is concentric with said edge face (4) of said
lens blank (1), and a shoulder (21) forming a second complementary
control guide; said lens blank (1) being configured to be at least
partially lodged in said cavity (13) of said ring (10), said edge
face (4) of said lens blank (1) being configured to at least
partially make contact with said internal outline (20) of said ring
(10) and said at least one sloped portion (5) of said lens blank
(1) being configured to also make contact with said shoulder (21)
of said ring (10).
29. The assembly as claimed in claim 28, wherein said lens blank
(1) comprises a circular chamfer (5) forming said sloped portion,
which circular chamfer (5) has a slope comprised between about
20.degree. and about 45.degree., and said ring (10) comprises a
ridge (22) defined by said shoulder (21), said circular chamfer (5)
bearing against said ridge (22) when said lens blank (1) is
partially lodged in said ring (10).
30. The assembly as claimed in claim 28, wherein said lens blank
(1) further comprises a third mechanical positioning guide (6) in
said generally circular edge face (4), a flat for example, and said
positioning ring (10) comprises a third complementary control guide
(18, 19) in said internal outline (20), for example a right
portion, said third mechanical positioning guide (6) and said third
mechanical control guide (18, 19) being configured to immobilize
rotationally said lens blank (1) about an axis (Tz) passing through
said upper (32) and lower (33) faces of said lens blank (1),
relative to said ring (10), when said lens blank (1) is partially
lodged on said ring (10).
31. The assembly as claimed in claim 30, wherein said third
mechanical positioning guide (6) is located parallel to a
nasal-temporal axis of said lens blank (1) for forming said optical
lens.
32. The assembly as claimed in claim 28, wherein said positioning
ring (10) further comprises an injection channel (25) opening onto
said cavity (13) and said assembly further comprises a blocking and
holding pin (30) on which said lens blank (1) is configured to be
positionally blocked by virtue of a binding material injected
through said injection channel (25), said positioning ring (10)
then being interposed between said lens blank (1) and said blocking
and holding pin (30).
33. The assembly as claimed in claim 28, wherein said ring (10)
comprises a plurality of guiding blocks (16) regularly distributed
around said cavity (13) and defining said internal outline
(20).
34. The assembly as claimed in claim 28, wherein said at least one
sloped portion (5) of said lens blank (1) has an angle of
inclination (.alpha..sub.1, .alpha..sub.2, .alpha..sub.3) relative
to said edge face (4) of said lens blank (1), which angle of
inclination (.alpha..sub.1, .alpha..sub.2, .alpha..sub.3) is set so
as to increase contact between said lens blank (1) and said
positioning ring (10) depending on at least one preset
constraint.
35. The assembly as claimed in claim 34, wherein said angle of
inclination (.alpha..sub.1, .alpha..sub.2, .alpha..sub.3) of said
at least one sloped portion (5) is set depending on a
characteristic representative of a perimeter of contact between
said at least one sloped portion (5) of said lens blank (1) and
said shoulder (21) of said ring (10) in order to ensure the
stability of said lens blank (1) in said ring (10).
36. The assembly as claimed in claim 34, wherein said angle of
inclination (.alpha..sub.1, .alpha..sub.2, .alpha..sub.3) of said
at least one sloped portion (5) is set depending on a
characteristic representative of an optically useful zone of said
optical lens in order to ensure a preset aperture for said optical
lens.
37. The assembly as claimed in claim 35, wherein said angle of
inclination (.alpha..sub.1, .alpha..sub.2, .alpha..sub.3) of said
at least one sloped portion (5) is set depending on a
characteristic representative of an optically useful zone of said
optical lens in order to ensure a preset aperture for said optical
lens.
38. The assembly as claimed in claim 29, wherein said lens blank
(1) further comprises a third mechanical positioning guide (6) in
said generally circular edge face (4), a flat for example, and said
positioning ring (10) comprises a third complementary control guide
(18, 19) in said internal outline (20), for example a right
portion, said third mechanical positioning guide (6) and said third
mechanical control guide (18, 19) being configured to immobilize
rotationally said lens blank (1) about an axis (Tz) passing through
said upper (32) and lower (33) faces of said lens blank (1),
relative to said ring (10), when said lens blank (1) is partially
lodged on said ring (10).
Description
[0001] The invention relates to the field of manufacture of optical
lenses.
[0002] The invention more particularly relates to processes for
manufacturing such lenses having a first face and a second face
opposite the first face, comprising a step of positioning the
second face relative to the first face, for the machining of this
second face.
[0003] The invention furthermore relates to assemblies used to
manufacture such lenses.
[0004] Such manufacturing processes comprising a step of providing
a lens blank, also called a semi-finished lens blank, having a
preformed convex face and a concave face to be machined are already
known from European patent application EP 2 199 021.
[0005] The first face, or the front face here, of the lens is
formed by the face of the lens blank having a convex shape, and the
second face, or the back face here, of the lens is formed by the
face of the lens blank having a concave shape.
[0006] The manufacture of such a lens typically comprises steps in
which the surface of the lens blank is marked.
[0007] For example, this may involve points or crosses identifying
a particular point (for example the optical center of the lens or
the prism reference point for a progressive lens), axis lines (for
example indicating the horizontal axis along which astigmatism is
corrected) and shapes bounding particular zones (for example a near
vision zone or a far vision zone in the case of progressive optical
lenses). Likewise, it may be necessary to produce marks allowing
the lens to be identified, or other commercial marks.
[0008] These marks are generally produced by micro-engraving or are
printed marks, called temporary marks.
[0009] The lens blank thus marked is then mounted on what is
referred to as a supporting ring.
[0010] This ring is annular and comprises on an upper edge a
plurality of visual control guides.
[0011] The operator may thus roughly position the lens blank on the
ring visually by comparing the positions of the marks on the lens
blank and the visual guides on the ring. If needs be, the operator
may modify the position of the lens blank on the ring by moving it
translationally in three directions relative to three axes of a
basic orthonormal coordinate system, and in rotation also in three
directions defined about each of the three axes, respectively.
[0012] The lens blank is then fastened to this ring and to a
blocking pin by way of a binding material, here what is referred to
as a fusible metal, extending from the front face of the lens blank
as far as this blocking pin.
[0013] The ring is thus interposed between the lens blank and the
blocking pin.
[0014] The blocking pin, together with the ring and the lens blank,
is mounted on a blocking and controlling apparatus, which apparatus
comprises an imaging device, also called a video camera, configured
to image both the control guides of the ring and the marks on the
lens blank.
[0015] The apparatus thus determines a first position of the lens
blank relative to the ring, and more precisely of the marked convex
face of the lens blank, and then determines a positioning error by
comparing this first position to a preset position of the lens
blank relative to the ring.
[0016] The first position of the lens blank corresponds to the
actual position of the convex face of the lens blank relative to
the ring and the positioning error is representative of corrections
that must be made to a surface file of the concave face. This
surface file is a file used in the machining of the concave face of
the lens blank, which file is loaded into a machine tool to machine
this concave face.
[0017] The blocking and controlling apparatus therefore transmits
this positioning error and/or these coordinate corrections to a
machine tool configured to machine the concave face of the lens
blank on the basis of the corrected surface file, in order to form
the front face of the optical lens.
[0018] The invention aims to provide a process for manufacturing
optical lenses, comprising a step of positioning the back face
relative to the front face of this lens, which allows positioning
errors to be limited, or even almost completely prevented, and that
is simple, convenient and economical.
[0019] Thus, the subject of the invention, according to a first
aspect, is a process for manufacturing an optical lens having a
first face and a second face opposite said first face, comprising a
step of positioning said second face relative to said first face
for the machining of said second face, which positioning step
comprises steps of: [0020] providing a lens blank for forming said
optical lens, which lens blank has an upper face for forming said
first face, a lower face, opposite said upper face, for forming
said second face, and at least one positioning guide; [0021]
providing a positioning ring having at least one control guide;
[0022] mounting said lens blank on said positioning ring; [0023]
positionally blocking said lens blank on a blocking and holding
pin, said positioning ring then being interposed between said lens
blank and said blocking and holding pin;
[0024] characterized in that said lens blank comprises a generally
circular edge face forming a first mechanical positioning guide and
at least one sloped portion forming a second mechanical positioning
guide, said at least one sloped portion being located between said
generally circular edge face and said upper face; said positioning
ring has a generally cylindrical shape and comprises a cavity
defining a generally circular internal outline forming a first
complementary control guide, which internal outline is concentric
with said edge face of said lens blank, and a shoulder forming a
second complementary control guide; and
[0025] said step of mounting said lens blank on said ring comprises
the step of at least partially lodging said lens blank in said
cavity of said ring, said edge face of said lens blank at least
partially making contact with said internal outline of said ring
and said at least one sloped portion of said lens blank also making
contact with said shoulder of said ring.
[0026] The process according to the invention has the advantage of
simplifying the step of positioning the second face relative to the
first face of the lens with a view to machining this second face,
while improving the performance of this positioning by almost
completely, or even completely, eliminating any possible
positioning errors.
[0027] More specifically, the positioning step is made easier by
virtue of the configurations of the lens blank and of the ring, and
more precisely by virtue of the first and second mechanical
positioning guides on this lens blank and of the first and second
complementary mechanical control guides on this ring.
[0028] The first group formed from the first mechanical positioning
and control guides, in other words the generally circular edge face
and the generally circular internal outline that is concentric with
this edge face, allows the lens blank to be reliably positioned on
the ring, i.e. without subsequent checking being required (whether
by eye by an operator or by a video camera). This lens blank is
positioned in two translational directions corresponding to two of
the axes of a basic orthonormal coordinate system, namely the
directions Tx and Ty that here are located in one and the same
first plane, referred to as the horizontal plane, and in two
rotational directions, namely Rx and Ry, defined about the above
translational directions, respectively.
[0029] The second group formed from the second mechanical
positioning and control guides, in other words the one or more
sloped portions and the shoulder, allows the lens blank to be
reliably positioned on the ring, i.e. without subsequent checking
being required (whether by eye by an operator or by a video
camera). The lens blank is essentially positioned in another
translational direction corresponding to the third axis of the
basic orthonormal coordinate system, namely the direction Tz, which
here is located in a second plane, referred to as the vertical
plane, but also in the two translational directions Tx and Ty.
[0030] Once at least partially lodged on the ring, the lens blank
is therefore in what is referred to as its definitive position, at
least in the translational directions Tx, Ty and Tz and in the
rotational directions Rx and Ry, for the machining of the second
face of the lens. The position of the lens blank on the ring is
here independent of the geometry of the upper face of the lens
blank.
[0031] In contrast to the visual control guides of the ring used in
the prior-art process, the first and second mechanical control
guides of the ring used in the process according to the invention
do not play an essential role in aiding visual positioning by an
operator or an imaging device. Specifically, these first and second
mechanical control guides on this ring rather correspond to
complementary positioning guides in that each plays a practical
role in and during the partial lodging of the lens blank on the
ring.
[0032] It will be noted that since the positioning step takes place
before the lower face of the lens blank is machined to form the
second face of the lens, it is more precisely the lower face of the
lens blank that is positioned relative to the first face (since in
general the upper face of the lens blank has already been shaped,
for example by machining, in order to form the first face of the
lens).
[0033] According to preferred simple, convenient and economical
features of the process according to the invention, said lens blank
furthermore comprises a third mechanical positioning guide in said
generally circular edge face, a flat for example, and said
positioning ring comprises a third complementary control guide in
said internal outline, for example a right portion, said third
mechanical positioning guide and said third mechanical control
guide being configured to immobilize rotationally said lens blank
about an axis passing through said upper and lower faces of said
lens blank, relative to said ring, when said lens blank is mounted
on said ring.
[0034] The third group formed from the third mechanical positioning
and control guides, for example the flat and the right portion,
allows the lens blank to be reliably positioned on the ring, i.e.
without subsequent checking being required (whether by eye by an
operator or by a video camera). The lens blank is positioned in
another rotational direction defined about the translational
direction Tz, namely Rz.
[0035] Once at least partially lodged on the ring, the lens blank
is therefore in what is referred to as its definitive position, in
all the translational directions Tx, Ty and Tz and rotational
directions Rx, Ry and Rz, without it being necessary to inspect
this position, for the machining of the second face of the
lens.
[0036] According to preferred simple, convenient and economical
features of the process according to the invention, said lens blank
furthermore comprises a third mechanical or visual positioning
guide in said generally circular edge face or at the periphery of
said upper face; and said process furthermore comprises a step of
visually or mechanically controlling the angular position of said
lens blank relative to said ring, which angular position is
measured relative to an axis passing through said upper and lower
faces of said lens blank, when said lens blank is mounted on said
ring; and a step of determining a possible angular position
error.
[0037] Here, in order to ensure the definitive position of the lens
blank relative to the ring is correct, only in the other rotational
direction defined about the translational direction Tz, namely Rz,
a step of visual or mechanical inspection of the angular position
of the lens blank is required. This step of visual or mechanical
inspection may be carried out by a mechanical probe or by eye by an
operator or even by an imaging device.
[0038] According to preferred, simple, convenient and economical
features of the process according to the invention: [0039] the
process furthermore comprises the step of machining said lower face
of said lens blank in order to form said second face of said
optical lens; [0040] the process furthermore comprises steps of
trimming said lens blank to a preset diameter, polishing said
previously machined second face and engraving said previously
machined second face; [0041] the step of coating said upper face of
said lens blank before said step of mounting said lens blank on
said positioning ring; [0042] said positioning ring furthermore
comprises an injection channel opening onto said cavity and said
step of positionally blocking said lens blank on said blocking and
holding pin comprises the step of injecting a binding material, for
example a metal, into said injection channel; [0043] said step of
providing said lens blank comprises steps of edging at least
partially the outline of said lens blank in order to form said
generally circular edge face and thus form said first mechanical
positioning guide of said lens blank; chamfering at least partially
one portion of said lens blank, which portion is located between
said generally circular edge face and said convex face, in order to
form said at least one sloped portion and thus form said second
mechanical positioning guide of said lens blank; and machining said
third mechanical positioning guide of said lens blank into said
outline of said lens blank; and/or [0044] said step of providing
said lens blank furthermore comprises a step of machining said
upper face of said lens blank in order to form said upper face of
said optical lens.
[0045] Another subject of the invention, according to a second
aspect, is an assembly comprising a lens blank for forming an
optical lens having a first face and a second face opposite said
first face, and a positioning ring on which said lens blank is
mounted, which lens blank has an upper face for forming said first
face and a lower face, opposite said upper face, for forming said
second face; characterized in that said lens blank furthermore
comprises a generally circular edge face forming a first mechanical
positioning guide and at least one sloped portion forming a second
mechanical positioning guide, said at least one sloped portion
being located between said generally circular edge face and said
upper face; said positioning ring has a generally cylindrical shape
and comprises a cavity defining a generally circular internal
outline forming a first complementary control guide, which internal
outline is concentric with said edge face of said lens blank, and a
shoulder forming a second complementary control guide; said lens
blank being configured to be at least partially lodged in said
cavity of said ring, said edge face of said lens blank being
configured to at least partially make contact with said internal
outline of said ring and said at least one sloped portion of said
lens blank being configured to also make contact with said shoulder
of said ring.
[0046] The assembly according to the invention has the advantage of
simplifying positioning of the second face relative to the first
face of the lens with a view to machining this second face, while
improving the performance of this positioning by almost completely,
or even completely, eliminating any possible positioning
errors.
[0047] More specifically, the positioning is made easier by virtue
of the configurations of the lens blank and of the ring, and more
precisely by virtue of the first and second mechanical positioning
guides on this lens blank and of the first and second mechanical
control guides on this ring.
[0048] The first group formed from the first mechanical positioning
and control guides, in other words the generally circular edge face
and the generally circular internal outline that is concentric with
this edge face, allows the lens blank to be reliably positioned on
the ring, i.e. without subsequent checking being required (whether
by eye by an operator or by a video camera). The lens blank is
positioned in two translational directions corresponding to two of
the axes of a basic orthonormal coordinate system, namely the
directions Tx and Ty that here are located in one and the same
plane, referred to as the horizontal plane, and in two rotational
directions, namely Rx and Ry, defined about the above translational
directions, respectively.
[0049] The second group formed from the second mechanical
positioning and control guides, in other words the one or more
sloped portions and the shoulder, allows the lens blank to be
reliably positioned on the ring, i.e. without subsequent checking
being required (whether by eye by an operator or by a video
camera). The lens blank is essentially positioned in another
translational direction corresponding to the third axis of the
basic orthonormal coordinate system, namely the direction Tz, which
here is located in a plane, referred to as the vertical plane, but
also in the two translational directions Tx and Ty.
[0050] Once at least partially lodged on the ring, the lens blank
is therefore in what is referred to as its definitive position, at
least in the translational directions Tx, Ty and Tz and in
rotational directions Rx and Ry, for the machining of the second
face of the lens. The position of the lens blank on the ring is
here independent of the geometry of the upper face of the lens
blank.
[0051] In contrast to the visual control guides of the ring used in
the prior-art process, the first and second mechanical control
guides of the ring of the assembly according to the invention do
not play an essential role in aiding visual positioning by an
operator or an imaging device. Specifically, these first and second
mechanical control guides on this ring rather correspond to
complementary positioning guides in that each plays a practical
role in the partial lodging of the lens blank on the ring.
[0052] It will be noted that since the positioning takes place
before the lower face of the lens blank is machined to form the
second face of the lens, it is more precisely the lower face of the
lens blank that is positioned relative to the first face (since in
general the upper face of the lens blank has already been shaped,
for example by machining, in order to form the first face of the
lens).
[0053] According to preferred, simple, convenient and economical
features of the assembly according to the invention: [0054] said
lens blank comprises a circular chamfer forming said sloped
portion, which circular chamfer has a slope comprised between about
20.degree. and about 45.degree., and said ring comprises a ridge
defined by said shoulder, said circular chamfer bearing against
said ridge when said lens blank is partially lodged in said ring;
[0055] said lens blank furthermore comprises a third mechanical
positioning guide in said generally circular edge face, a flat for
example, and said positioning ring comprises a third mechanical
control guide in said internal outline, for example a right
portion, said third mechanical positioning guide and said third
mechanical control guide being configured to immobilize
rotationally said lens blank about an axis passing through said
upper and lower faces of said lens blank, relative to said ring,
when said lens blank is partially lodged on said ring; so that the
third group formed from the third mechanical positioning and
control guides, the flat or right portion for example, allows the
lens blank to be reliably positioned on the ring, i.e. without
subsequent checking being required (whether by eye by an operator
or by a video camera), in another rotational direction defined
about the translational direction Tz, namely Rz; [0056] said third
mechanical positioning guide is located parallel to a
nasal-temporal axis of said lens blank for forming said optical
lens; [0057] said positioning ring furthermore comprises an
injection channel opening onto said cavity and said assembly
furthermore comprises a blocking and holding pin on which said lens
blank is configured to be positionally blocked by virtue of a
binding material injected through said injection channel, said
positioning ring then being interposed between said lens blank and
said blocking and holding pin; and/or [0058] said ring comprises a
plurality of guiding blocks regularly distributed around said
cavity and defining said internal outline.
[0059] According to other preferred, simple, convenient and
economical features of the assembly according to the invention:
[0060] said at least one sloped portion of said lens blank has an
angle of inclination relative to said edge face of said lens blank,
which angle of inclination is set so as to increase contact between
said lens blank and said positioning ring depending on at least one
preset constraint; [0061] said angle of inclination of said at
least one sloped portion is set depending on a characteristic
representative of a perimeter of contact between said at least one
sloped portion of said lens blank and said shoulder of said ring in
order to ensure the stability of said lens blank in said ring;
and/or [0062] said angle of inclination of said at least one sloped
portion is set depending on a characteristic representative of an
optically useful zone of said optical lens in order to ensure a
preset aperture for said optical lens.
[0063] The optically useful zone is the zone of the optical lens
that has the optical features associated with the prescription of
the wearer. It is generally a question of a zone of the lens that
is located in a spectacle frame when this lens is cut to the shape
of the frame and fitted in the latter.
[0064] The aperture of the optical lens is representative of the
size of the optically useful zone.
[0065] The subject matter of the invention will now be explained by
way of a description of one embodiment thereof, given below, by way
of nonlimiting illustration, with reference to the appended
drawings, in which:
[0066] FIG. 1 schematically shows a step of the process for
manufacturing an optical lens, according to the invention, here
machining of the upper face and the periphery of a lens blank, in
order to form the first face of the lens;
[0067] FIG. 2 schematically shows another step of the process for
manufacturing the optical lens, here mounting and blocking the lens
blank on a positioning ring in order to position the lower face of
the lens blank relative to the first face;
[0068] FIG. 3 schematically shows yet another step of the process
for manufacturing a lens, here machining of the lower face of the
lens blank, in order to form the second face of the optical
lens;
[0069] FIG. 4 is a perspective view of the lens blank, after the
machining step illustrated in FIG. 1;
[0070] FIG. 5 schematically shows a top view of the lens blank in
the positioning ring, as illustrated in FIG. 2;
[0071] FIGS. 6 and 7 are, respectively, perspective views of the
positioning ring in isolation and of this ring when the lens blank
is mounted therein, as illustrated in FIG. 2;
[0072] FIG. 8 is a schematic partial view of the cross section
referenced VIII-VIII in FIG. 7;
[0073] FIG. 9 is a block diagram illustrating various operating
steps of the process for manufacturing the optical lens, especially
comprising the step illustrated in FIG. 1;
[0074] FIG. 10 is a block diagram illustrating in detail one of the
steps shown in FIG. 9, namely the machining of mechanical guides
into the lens blank;
[0075] FIG. 11 is a block diagram illustrating other operating
steps of the process for manufacturing the optical lens, especially
comprising the steps illustrated in FIGS. 2 and 3; and
[0076] FIGS. 12 to 15 each show the lens blank in FIGS. 2 and 3, as
seen from in front and above, according to a plurality of variant
embodiments of one sloped portion that it comprises.
[0077] FIGS. 1 and 3 illustrate various operating steps of a
process for manufacturing an optical lens 1.
[0078] Here, the optical lens 1 is an optical lens configured to
form a spectacle lens intended to be fitted in a pair of
spectacles.
[0079] This optical lens has a first face, here corresponding to a
front face 2 that has a convex shape, and a second face, here
corresponding to a back face 3 that has a concave shape. This back
face 3 may have a complex surface (a "free-form" or "digital"
surface) that, especially because of the large altitude variations,
for example combined with a torus and a progression, of the surface
requires particularly precise machining and more precisely
surfacing that is difficult to achieve.
[0080] It is necessary to position correctly the optical lens 1,
and more precisely its (as yet unmachined) back face 3 relative to
its (already machined) front face 2 in order to produce the back
face 3 of the optical lens 1 in accordance with the desired
ophthalmic prescription.
[0081] The optical lens is formed from a lens blank, also
referenced 1, comprising a solid body generally molded from
plastic.
[0082] This lens blank 1, in the raw state, also called the first
semi-finished lens blank, has an upper face here corresponding to a
convex face 32 and a lower face here corresponding to a concave
face 33, each being intended to form the front face 2 and the back
face 3 of the lens, respectively.
[0083] FIG. 1 illustrates the machining of the convex face 32, also
called the front face, of the lens blank 1 and the machining of
mechanical positioning guides on this lens blank 1.
[0084] FIG. 2 illustrates the positioning of the lens blank 1 in a
positioning ring 10, after the machining steps illustrated in FIG.
1.
[0085] FIG. 3 for its part illustrates the machining of the concave
face 33 of the lens blank 1.
[0086] The process for manufacturing the optical lens from the lens
blank will be described in greater detail below with reference to
FIGS. 9 to 11, which illustrate various operating steps of this
manufacturing process, and with reference to FIGS. 1 to 3, which
illustrate the actual implementation of certain of these steps.
[0087] The lens blank 1 that allows the optical lens to be formed,
the positioning ring 10 and the interaction between this lens blank
1 and this ring 10 will now be described in greater detail.
[0088] FIG. 4 illustrates the lens blank 1 such as shown in FIG. 2,
in other words after its convex face 32 and the mechanical
positioning guides have been machined.
[0089] The lens blank 1 here comprises, opposite its concave face
33, the front face 2 of the optical lens.
[0090] The lens blank 1 furthermore comprises an edge face 4 that
is generally circular, a flat 6 that is located in a portion of
this edge face 4, and a chamfer 5 forming a sloped portion that
here is beveled and generally circular. This chamfer 5 is located
between the edge face 4 and the front face 2.
[0091] Here, the chamfer 5 has a slope, or angle of inclination,
relative to the edge face 4 of the lens blank 1, comprised between
about 20.degree. and about 45.degree..
[0092] This angle of inclination is set so as to increase contact
between the lens blank 1 and the positioning ring 10 depending on
at least one preset constraint (see below with reference to FIGS.
12 to 15). The lens blank 1 thus machined forms what is referred to
as a second semi-finished lens blank. The first semi-finished lens
blank is the lens blank 1 in its raw state, as indicated above.
[0093] The generally circular edge face 4 forms a first mechanical
positioning guide, the chamfer 5 forms a second mechanical
positioning guide and the flat 6 forms a third mechanical
positioning guide, for positioning the lens blank (second
semi-finished lens blank) 1 in the positioning ring 10.
[0094] FIG. 6 illustrates the positioning ring 10 in isolation.
[0095] This ring 10, which has a generally cylindrical shape,
comprises a body 11, here made of aluminum, provided with a
cylindrical lateral wall 12, an upper edge 15 and a cavity 13
opening onto either side of the ring 10.
[0096] This ring 10 furthermore comprises four guiding blocks 16
protruding from the upper edge 15, which guiding blocks 16 are
configured to form an outline 20, internal to the ring 10, which is
generally circular.
[0097] The guiding blocks 16 are regularly distributed along the
upper edge 15.
[0098] The ring 10 also comprises a generally circular shoulder 21
defining a ridge, itself generally circular, which shoulder 21 is
located between the upper edge 15 and a bottom wall 23.
[0099] This bottom wall 23 is provided with a central aperture 14
opening onto the exterior of the ring 10 and a beveled portion 24
located between this aperture 14 and the bottom wall 23.
[0100] The ring 10 furthermore comprises another guiding block 18
different from the guiding blocks 16 in that this other block 18
has a right portion 19 on the side of the cavity 13 and therefore
in the generally circular internal outline 20.
[0101] This other block 18 is located between two guiding blocks
16.
[0102] The ring 10 furthermore comprises an injection channel 25
that runs through the body 11 and opens onto the cavity 13, as far
as the orifice 14.
[0103] The generally circular internal outline 20 forms a first
complementary control guide, the shoulder 21 and more precisely the
ridge 22 form a second complementary control guide and the right
portion 19 forms a third complementary control guide.
[0104] The positioning ring 10 is unitarily formed.
[0105] FIGS. 5 and 7 show the lens blank 1 illustrated in FIG. 4
partially lodged in the positioning ring 10 illustrated in FIG. 6
from different viewing angles. FIG. 5 is a schematic view.
[0106] FIG. 7 also illustrates the various directions of
translational movement of the lens blank 1 in the ring 10, namely
Tx, Ty and Tz, corresponding to the three axes of a basic
orthonormal coordinate system, and the directions of rotational
movement about each of these translational directions,
respectively, namely Rx, Ry and Rz.
[0107] It may be seen that the translational directions Tx and Ty
are here located in one and the same plane, referred to as the
horizontal plane, and that these axes Tx and Ty extend in the
diameter of the lens blank 1 whereas the translational direction Tz
corresponds substantially to the thickness of the lens blank 1 and
here is located in what is referred to as a vertical plane (i.e.
orthogonal to the plane comprising the axes Tx and Ty).
[0108] FIG. 8 for its part shows the lens blank 1, partially lodged
in the ring 10, in the cross section referenced VII-VII in FIG.
7.
[0109] It will be noted that the internal outline 20 of the ring 10
is concentric with the edge face 4 of the lens blank 1.
[0110] It will further be noted that when the lens blank 1 is
partially lodged in the cavity 13 of the ring 10, the edge face 4
of the lens blank 1 makes contact with the internal outline 20 of
the ring and more precisely with curved internal portions of the
guiding blocks 16.
[0111] Furthermore, the chamfer 5 of the lens blank 1 also at least
partially makes contact with the ridge 22 defined by the shoulder
21 of the ring 10.
[0112] Furthermore, the flat 6 faces, or even makes contact with,
the right portion 19 of the other guiding block 18 of the ring
10.
[0113] The first group formed from the first mechanical positioning
and complementary control guides, in other words said edge face 4
of the lens blank 1 and the internal outline 20 of the ring 10,
allow the lens blank 1 to be reliably positioned, in the
translational directions Tx, Ty and in the rotational directions
Rx, Ry, on the ring 10.
[0114] The second group formed from the second mechanical
positioning and complementary control guides, in other words the
chamfer 5 of the lens blank 1 and the ridge 22 of the shoulder 21
of the ring 10, allow the lens blank 1 to be reliably positioned,
in the translational direction Tz and also in the translational
directions Tx, Ty, on the ring 10.
[0115] Furthermore, the third group formed from the third
mechanical positioning and complementary control guides, in other
words the flat 6 and the right portion 19 of the other guiding
block 18 of the ring 10, allow the lens blank 1 to be reliably
positioned, in the rotational direction Rz, on the ring 10.
[0116] Thus, in the position of the lens blank 1 relative to the
ring 10 shown in FIGS. 5, 7 and 8, the lens blank 1 is in what is
referred to as its definitive position in all the translational
directions Tx, Ty, Tz and rotational directions Rx, Ry and Rz.
Simply positioning the lens blank 1 on the ring 10 therefore
ensures, as described in greater detail below, that the so-called
definitive position of the concave face 33 of the lens blank 1
relative to the front face 2 and therefore of the (as yet
unmachined) back face relative to the front face of the lens is
correct.
[0117] The process for manufacturing the optical lens will now be
described in greater detail with reference to FIGS. 9 to 11 and
also to FIGS. 1 to 3.
[0118] The process comprises the step 101 of providing a lens blank
SF1, which lens blank SF1 corresponds to the raw (first
semi-finished) lens blank such as described above. This lens blank
SF1 is made of plastic and has a convex face 32 and a concave face
33 that is not machined and results from molding.
[0119] The process comprises the step 102 of coating the concave
face 33, also called back face (BK face), of the lens blank SF1. It
is a question of applying to this concave face 33 a plastic film
(not shown) allowing said face 33 to be protected.
[0120] The process comprises the step 103 of blocking the concave
face 33 of the lens blank SF1. This blocking step is shown in FIG.
1, in which an assembly comprising the lens blank SF1, here
referenced 1, a blocking and holding pin 30 and a binding material
31 here formed of what is referred to as a fusible metal, is
shown.
[0121] In this step 103, the lens blank SF1 is mounted on a holder
(not shown) at the bottom of which the pin 30 is positioned.
[0122] This holder for example comprises an injection channel
through which the binding metal is injected in liquid form. Once
hardened, this metal 31 fastens the pin 30 to the lens blank SF1
via its concave face 33.
[0123] The process furthermore comprises the step 110 of machining
the convex face 32 of the lens blank SF1, also called the front
face. This machining step is also illustrated in FIG. 1, which
shows the convex face 32 of the lens blank SF1 and the zone to be
machined to form the front face 2 of the optical lens.
[0124] The process comprises the step 111 of machining the
mechanical positioning guides on the lens blank SF1, namely the
generally circular edge face 4, the chamfer 5 and the flat 6. These
three mechanical positioning guides produced in the lens blank SF1
allow, as indicated above and also below, the (second
semi-finished) lens blank SF2 to be positioned in the positioning
ring 10 both in the translational directions Tx, Ty and Tz and
rotational directions Rx, Ry and Rz.
[0125] This machining step 111 in particular comprises the step 121
of edging an outline of the lens blank SF1 to form the generally
circular edge face 4 and thus form the first mechanical positioning
guide of the lens blank SF1.
[0126] This machining step 111 furthermore comprises the step 122
of chamfering a portion of the lens blank SF1 (located between the
generally circular edge face 4 and the convex face 32) in order to
form a beveled portion and thus form the second mechanical
positioning guide of this lens blank SF1.
[0127] This machining step 111 also comprises the step 123 of
machining the flat 6 in the outline of the lens blank SF1 in order
to form a third mechanical positioning guide for this lens blank
SF1.
[0128] The machining of the guide in Rz may result in something
other than a flat 6, especially shown in FIG. 4, and as a variant
this guide may be a notch produced in the generally circular edge
face 4.
[0129] The steps 110 and 111 may be carried out in one and the same
machine tool, in one and the same machining operation or in two
successes operations, or in separate machines. The step 110 may be
implemented before step 111, or vice versa.
[0130] The convex face 32 of the lens blank SF1 and the mechanical
positioning guides are machined in the lens blank SF1 relative to
each other, and more precisely the convex face is produced relative
to the mechanical positioning guides or vice versa. This process
therefore allows a positional reference system to be created
between the convex face and the mechanical positioning guides.
[0131] This relationship is particularly simple to obtain since the
two machining steps are carried out at the same time, or
consecutively, in one and the same machine tool, which uses one the
same machining frame of reference and therefore positions the
surface and the positioning guides with high precision relative to
each other, or even one and the same surface file.
[0132] The process then comprises the step 112 of polishing the
front face of the lens blank SF1, which front face is then
representative of the front face 2 of the lens since the convex
face 32 has been machined.
[0133] The process also comprises the step 113 of unblocking the
concave face 33 of the lens blank SF1, which step 113 is similar to
the unblocking step 115 described above.
[0134] The lens blank SF2, also referred to as the second
semi-finished lens blank, is then obtained.
[0135] Once this second semi-finished lens blank has been produced,
the latter may for example be stored and is more often than not
sent to another site, especially for production of the back face 3
of the lens 1, by virtue of a different machine tool to that/those
used above.
[0136] The process for manufacturing this optical lens furthermore
comprises, as illustrated in FIG. 11, the step 131 of providing
this second semi-finish lens blank, in other words the lens blank
SF2.
[0137] The process comprises the step 132 of coating the front face
2 of the lens blank SF2. It is here a question of coating the front
face 2 with a plastic film (not shown).
[0138] The process comprises the step 133 of providing the
positioning ring described above, especially with reference to
FIGS. 5 to 8, and the step 134 of positioning the lens blank SF2 on
this ring 10, as may be seen in FIG. 2.
[0139] The lens blank SF2 is positioned on the ring 10 such that
this lens blank SF2 is partially lodged in the cavity 13 of this
ring 10, the edge face 4 of the lens blank SF2 making contact with
the internal outline 20 described by the cavity 13, and in
particular with the curved internal portions of the guiding blocks
16, the chamfer 5 of the lens blank SF2 also at least partially
making contact with the ridge 22 of the shoulder 21 of the ring 10,
and the flat 6 facing, or even making contact, with the internal
portion 19 of another guiding block 18 of this ring 10.
[0140] Thus, the first group formed from the edge face 4 and the
internal outline 20 allow the lens blank SF2 to be reliably, i.e.
without requiring subsequent checking, positioned on the ring 10 in
the translational directions Tx and Ty and in the rotational
directions Rx and Ry.
[0141] Furthermore, the second group formed from the chamfer 5 and
the ridge 22 of the shoulder 21 also allows the lens blank SF2 to
be reliably positioned on the ring 10, essentially in the
translational direction Tz but also in the translational directions
Tx and Ty.
[0142] Lastly, the third group formed from the flat 6 and the right
portion 19 also allow the lens blank SF2 to be reliably positioned
on the ring 10, in the other rotational direction Rz.
[0143] The lens blank SF2 thus positioned is therefore in a
definitive position that therefore corresponds to the positioning
of the as yet unmachined back face of the lens relative to the
front face 2, and here more precisely to the positioning of the
concave face 33 of the lens blank SF2 relative to the front face
2.
[0144] The process then comprises the step 135 of blocking the
front face 2 of the lens blank SF2 in order to block positionally
the lens blank SF2 in the ring 10. In this step 135, the lens blank
SF2 is mounted on the positioning ring 10 at the bottom of which
the blocking and holding pin 30 (identical to the holder 30 shown
in FIG. 1) is positioned.
[0145] A binding material 31 taking the form of a liquid metal is
injected through the injection channel 25 into the cavity 13
(between the front face 2 and the pin 30 and the bottom wall 23 of
the ring 10), and once hardened, this metal 31 fastens the pin 30
to the lens blank SF2 via its concave face 33.
[0146] The process may furthermore comprise the step 136 of
inspecting the position in the rotational direction Rz of the
concave face 33 of the lens blank SF2 relative to the front face
2.
[0147] In the example illustrated here, this inspection step 136 is
obsolete since, by virtue of the third mechanical positioning
guide, namely the flat 6, and by virtue of the third complementary
mechanical control guide, namely the internal portion 19, the
position of the lens blank SF2 in Rz is fixed, i.e. the lens blank
SF2 cannot move rotationally in Rz since it is immobilized in Rz in
its definitive position.
[0148] In the variants indicated above where it is not a question
of a flat 6 and a right internal portion 19 as shown in FIGS. 4 and
6, but merely a question of a notch produced in the lens blank SF2,
then this step 136 of inspecting the position of the lens blank SF2
in Rz in the ring 10 may be necessary.
[0149] This inspection step 136 may for example be carried out by
eye by an operator, or by virtue of a mechanical probe or even by
virtue of an imaging device such as a video camera.
[0150] This inspection step 136 may therefore comprise the step of
determining possible positioning errors in Rz and the step of
correcting these possible positioning errors.
[0151] This correction step is here carried out directly on a
surface file defining the back face 3 of the lens to be
obtained.
[0152] This inspection and optional correction step 136 therefore
furthermore optionally comprises a step of transmitting a corrected
file to a machine tool configured to produce the back face 3 of the
optical lens.
[0153] The process furthermore comprises the step 137 of machining
the concave face 33 of the lens blank SF2 to obtain the back face 3
of the optical lens 1.
[0154] This step is shown in FIG. 3 in which the lens blank SF2
blocked positionally on the pin 30 and the concave face 33 to be
machined of the lens blank SF2 to obtain the back face 3 of the
optical lens 1 may be seen.
[0155] The process furthermore comprises the step 138 of removing
the lens blank SF2 thus machined from the ring 10 then the step 139
of trimming this lens blank SF2. This trimming step is carried out
to a preset diameter.
[0156] The process furthermore comprises the step 140 of polishing
the back face 3 of the lens blank SF2 and the step 141 of
engraving, or marking by engraving, said back face 3 of the lens
blank SF2.
[0157] Lastly, the manufacturing process comprises the step 142 of
unblocking the front face 2 of the lens blank SF2 in order to make
the finished optical lens 1 available to be formed, subsequently,
into a finished spectacle lens (VF).
[0158] FIGS. 12 to 15 illustrate the lens blank 1 with various
variant embodiments of the chamfer 5.
[0159] In FIGS. 12 and 13, the lens blank 1 has a front face, here
a progressive face, and the chamfer 5 that it comprises has an
angle of inclination .alpha..sub.1 of about 45.degree. and an angle
of inclination .alpha..sub.2 of about 20.degree., respectively,
relative to the edge face 4 of the lens blank 1.
[0160] These distinct angles of inclination .alpha..sub.1 and
.alpha..sub.2 of the chamfer 5 are determined so as to increase
contact between the lens blank 1 and the positioning ring 10
depending on at least one preset constraint.
[0161] FIGS. 12 and 13 illustrate perimeters of contact 50 between
the lens blank 1 and the ring 10.
[0162] These perimeters of contact 50 are of different lengths
along the chamfer 5; and are representative of lengths of angular
sectors, denoted .theta..sub.1 and .theta..sub.2, passing through
the optical center or prism reference point or even the geometric
center P of the lens, from which sectors the length of the flat 6
of the lens blank 1 must be subtracted.
[0163] The perimeter of contact 50 between the shoulder of a given
ring and the chamfer 5 of angle of inclination .alpha..sub.1 is
representative of the smaller angular sector .theta..sub.1 which is
smaller than the angular sector .theta..sub.2 that represents the
perimeter of contact 50 between the shoulder of this given ring and
the chamfer 5 of angle of inclination .alpha..sub.2.
[0164] In other words, the percentage of contact between the lens
blank illustrated in FIG. 12 and the given ring is less than the
percentage of contact between the lens blank illustrated in FIG. 13
and this given ring.
[0165] Therefore, the lens blank illustrated in FIG. 13 will be
more stable in the given ring than the lens blank illustrated in
FIG. 12 for the same ring.
[0166] In FIGS. 14 and 15, the lens blank 1 has a front face, here
a regressive face, and the chamfer 5 that it comprises has an angle
of inclination .alpha..sub.1 of about 45.degree. and an angle of
inclination .alpha..sub.3 of about 30.degree., respectively,
relative to the edge face 4 of the lens blank 1.
[0167] These distinct angles of inclination .alpha..sub.1 and
.alpha..sub.3 of the chamfer 5 are also determined so as to
increase contact between the lens blank 1 and the positioning ring
10 depending on at least one preset constraint.
[0168] FIGS. 14 and 15 also illustrate perimeters of contact 50
between the lens blank 1 and the ring 10, these perimeters 50 here
having one and the same length substantially equal to the length of
the chamfer 5.
[0169] FIGS. 14 and 15 furthermore illustrate radii Rv
representative of the radius of an optically useful zone desired
for the optical lens and radii Rr.sub.1 and Rr.sub.2 representative
of the minimum radius of an optically useful zone obtained on the
lens blank 1 with the chamfer 5 produced in the latter, these radii
passing through the optical center or the prism reference point or
even the geometric center P of the lens.
[0170] The optically useful zone is the zone of the optical lens
that has the optical features associated with the prescription of
the wearer. It is generally a question of a zone of the lens that
is located in a spectacle frame when this lens is cut to the shape
of the frame and fitted in the latter.
[0171] This optically useful zone must not contain the chamfer
5.
[0172] The radius Rr.sub.1 obtained with a chamfer 5 of angle of
inclination .alpha..sub.1 is smaller than the radius Rr.sub.2
obtained with a chamfer 5 of angle of inclination
.alpha..sub.3.
[0173] In other words, the diameter of the optical lens obtainable
with a chamfer 5 of angle of inclination .alpha..sub.3 is larger
than the diameter of the optical lens obtainable with a chamfer 5
of angle of inclination .alpha..sub.1.
[0174] Therefore, the lens that can be obtained from the lens blank
illustrated in FIG. 15 has a larger aperture than the lens
obtainable with the lens blank illustrated in FIG. 14.
[0175] The aperture of the optical lens is representative of the
size of the optically useful zone.
[0176] The two constraints given above, namely the stability of the
lens blank in a given ring and the aperture of the lens, may be
used individually or in combination to determine the angle of
inclination of the chamfer produced in the lens blank.
[0177] It will be noted that in the examples given above the lens
blanks had progressive and regressive surfaces, but lens blanks
with toroidal surfaces could also be used.
[0178] More generally, the angle of inclination of the chamfer
produced in the lens blank is advantageously determined once the
lens blank has a surface that is no longer axisymmetric.
[0179] The angle of inclination is determined before steps 110 and
111 of machining the front face and the guides in the lens
blank.
[0180] The angle of inclination is for example set when the
geometry of the lens and the geometry of the guides in the lens
blank are defined for a given ring.
[0181] The angle of inclination is for example determined by
iterative calculation, by calculating the perimeter of contact
between the chamfer and the shoulder of a given ring until an angle
of inclination is obtained that allows a given percentage of
contact, for example higher than about 55% of the perimeter of
contact between the chamfer and the shoulder, to be achieved; with
the aim of meeting the stability constraint.
[0182] As a variant or enhancement, the angle of inclination is for
example determined by iterative calculation, by calculating the
resultant radius of the chamfered lens blank until an angle of
inclination is obtained that allows a resultant radius that is at
least equal to or even larger by about 1 mm than a given lens
radius to be achieved, for example higher than about 55% of the
perimeter of contact between the chamfer and the shoulder; with the
aim of meeting the aperture constraint.
[0183] As variants (not illustrated): [0184] the first face of the
lens blank to be machined is not the front face but rather the back
face, the front face therefore being machined next; more generally,
the expressions "first face" and "second face" may refer to either
face, independently of its position (front or back) and
independently of whether said face is concave or convex in shape;
[0185] the sloped portion is not a beveled or conical portion but
rather a portion taking the form of a fillet or shoulder, and here
the term "chamfer" or "molding" is understood to mean a sloped
portion taking any one of these forms; [0186] the positioning ring
does not have a generally cylindrical shape but rather a generally
rectangular shape, and this ring may have more or fewer guiding
blocks; [0187] the chamfer is not produced in the entire outline of
the lens blank but only in one portion of the outline, or even in a
plurality of portions of the outline; [0188] the third mechanical
positioning guide in the lens blank is not a flat or a notch, but
rather a mark produced by engraving the periphery of the front
face; [0189] the lens blank is not removed from the ring and the
process does not comprise a step of trimming the lens blank to a
set diameter; and the engravings produced in the concave face of
the lens blank are positioned relative to the chamfer; and the step
of engraving the concave face of the lens blank is carried out
before the trimming step and/or polishing step, i.e. when the lens
blank is mounted in the ring; [0190] the back face of the lens does
not comprise temporary or permanent markings but it is rather the
front face of the lens that has them; [0191] the steps of
unblocking the lens blank and removing the lens blank from the ring
are carried out before the step of machining the back face; [0192]
the correction step is not carried out directly on the surface file
defining the back face 3 of the lens to be obtained but rather on
the angular position of a shaft of the machine tool; and/or [0193]
the binding material is different from an injected liquid metal, it
instead being a question of a liquid wax or a mechanical fastening
device.
[0194] It is recalled more generally that the invention is not
limited to the examples described and shown.
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